1. Field of the Invention
The invention relates to a magnet embedded rotor and a method of manufacturing the magnet embedded rotor.
2. Description of the Related Art
There has been known an interior permanent magnet motor (IPM motor) having a structure in which field permanent magnets are embedded in a rotor. As a method of manufacturing a magnet embedded rotor used in such an IPM motor, a method described in Japanese Patent Application Publication No. 2010-193587 (JP 2010-193587 A) has been known. In this method, a cylindrical rotor having a plurality of magnet insertion holes is prepared, magnetic bodies are embedded in the magnet insertion holes, and then a magnetizing device is arranged so as to cover the outer periphery of the rotor. Then, magnetic flux is supplied to the inside of the rotor from the outer peripheral face of the rotor by the magnetizing device, so that the magnetic bodies embedded in the rotor are magnetized to be turned into filed permanent magnets.
As described in JP 2010-193587 A, when the magnetic flux is supplied from the outer peripheral face of the rotor, the amount of magnetic flux that can be supplied to the magnetic bodies embedded in the rotor is determined based on the surface area of the outer peripheral face of the rotor and the amount of magnetic flux per unit area, which can be supplied by the magnetizing device. There is a limit on the amount of magnetic flux per unit area, which can be supplied by the magnetizing device. Therefore, if the area of the outer peripheral face of the rotor is small relative to the area of the surfaces of the magnetic bodies to be magnetized, it is difficult to supply a sufficient amount of magnetic flux to the magnetic bodies. As a result, the magnetization ratio of the permanent magnets decreases.
When the magnetic flux is supplied from the outer peripheral face of the rotor, a radially inside portion of the rotor is supplied with a smaller amount magnetic flux than a radially outside portion of the rotor. Therefore, when the magnetic bodies are embedded in a radially inside portion of the rotor, it is difficult to supply a sufficient amount of magnetic flux to the magnetic bodies. As a result, the magnetization ratio of the permanent magnets decreases.
If the magnetization ratio of the permanent magnets decreases due to these factors, a sufficient amount of magnetic flux is not generated by the permanent magnets, and thus the magnetic flux density in the outer peripheral face of the rotor decreases. This leads to a reduction in the amount of effective magnetic flux interlinking with a stator coil of a motor, and constitutes a factor causing a decrease in the motor output torque.